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From: "Jukka K. Korpela" <jkorpela@cs.tut.fi>
Newsgroups: comp.lang.javascript
Subject: Re: Explicit zero-initialization of vars
Date: Wed, 28 Dec 2011 15:44:05 +0200
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2011-12-28 10:53, Archos wrote:

> Is it recommended make zero-initialization of vars explicit?

There is no implicit zero-initialization. If you declare a variable 
without initializing it, its initial value is the special value 
undefined, of the special type undefined.

> By example:
>
> `var i = 0`  instead of `var i` // for an integer
> `var s = ""` instead of `var s` // for a string

Without the initializers (= 0 and = ""), both i and s would come to life 
with the value undefined. It's not an integer value, it's no a string 
value, it's - of type undefined. You can see this if you check out this:

var i;
alert(i);
alert(typeof i);

It is generally a good idea to initialize a variable on declaration, if 
a natural and useful initial value can be assigned to it, such as 0 for 
a counter or "" for a variable into which some string will be composed 
by catenating strings.

It is not a good idea to initialize a variable with a dummy value just 
to make it initialized. Every variable _is_ initialized by language 
rules in JavaScript, and the special value undefined is often more 
useful than a dummy neutral value like 0 or "". If your code runs wild 
and uses the value of a variable to which no proper value has been 
assigned, it's better to "see" the variable value as undefined, as it 
logically is.

-- 
Yucca, http://www.cs.tut.fi/~jkorpela/